Olfaction and Taste Flashcards
1
Q
perspective
A
- smell and taste are the least well understood of the special senses- combine with orosomatosensory combine to create perception of flavor although olfaction in the dominant component
- both are critical for physiology of lower mammals- repro phys, food intake, social behavior
- less critical in humans, impact on QOL
- disorders can be profoundly distressing as well as harbingers of more general disease states
2
Q
problem for analysis
A
- the olfactory system has the capacity to discriminate among literally millions of odorants including those never smelled before
- gustatory system also open ended in its capacity to discriminate among compounds
- both maintain this despite death of old receptor elements and recruitment of new
- how do we maintain perceptual stability?
3
Q
basic peripheral and central components
A
- receptor cells that transduce odorant stimuli are bona fide neurons
- cell bodies are in OE
- in humans the OE lies in the poesterodorsal part of the nasal cavity below the cribiform plate on the nasal septum and lateral nasal wall
- the OE neurons relay information via axonal projections through the cribiform plate to the OB
- OB is first relay in the sensory chain
4
Q
pathways for olfactory processing
A
- from receptors to bulb
- to olfactory bulb targets
- pyriform cortex, olfactory tuberle
- amygdala-to orbitofrontal cortex (emotion), thalamus, hypothalamus (thalamus and OF cortex communicate
- entorhinal cortex-to hippocampus-memories
5
Q
OE
A
- basal cells, neurons, supporting cells
- neurons are bipolar with an apical dendrite ending in a knob with immotile cilia
- each neuron has thin unmyelinated axon (C) that projects to bulb
- cilia have OR
- basal cells are self renewing and replace old sensory neurons- use old axon tracts
- pseudostratified
6
Q
neurogenesis in OE
A
- basal cells continuously undergo mitotic division in a stem cell mode
- sensory neurons life span 30 days
- epithelial projections continually being broken down and re-forming
- symmetric or asymmetric division, or can create 2 new neurons if needed
- if no signal, dead
7
Q
signal transduction in olfactory neurons
A
- odorant delivered to the epithelium along the airstream
- odorant diffuses through mucus to cilia
- odorant interacts with G coupled receptor protein, which increases cAMP and opens channels for Ca to flow in
- results in depolarizing receptor potential
8
Q
diversity
A
- 1000 ORs in humans
- largest G grouped family in body
- allows for lots of receptor types
9
Q
generic olfactory receptor
A
- 7 transmembrane domains
- aa seq homology
10
Q
zonal distribution patterns
A
- neurons expressing a particular OR are limited to a particular region
- rodent-4
- spatial pattern makes a code
- ORs are slightly promiscuous
11
Q
receptor expression patterns
A
- underly coding
- each neuron only has one receptor but that receptor isn’t finely tuned
- within a zone, neurons expressing one type of OR can be homogeneously distributed or have a clustered distribution pattern
12
Q
responses of olfactory neurons
A
- single unit recordings show that they are broadly tuned
- diversity of physiologically defined types of olfactory neurons parallels number of ORs
- the OR on a neuron determines the responsiveness of that neuron
- any one OR is broadly tuned to respond to a lot of different odorants that share a common molecular feature
13
Q
spatial activity
A
- each odorant has a unique pattern of spatial activity
- there are inherent differences between areas of the epithelium and their response to odorants
- these inherent differences reflect distribution of ORs
14
Q
laminar organization
A
- bulb is most rostral part of CNS
- tubular in shape and the cells and their neuropil are arranged in concentric layers like an onion
- glomerular, external plexiform, mitral cell, granule cell
- mitral and tufted cells are the relay neurons that project to olfactory cortex
- periglomuerular cells and granule cells are inhibitory interneurons that modulate activity of the mitral tufted cells
- periglomerular are outmost shell of neurons
- cluster around glomeruli
- glomerulus is fundamental unit of anatomical and physiological organization in the bulb
15
Q
projection of the epithelium onto olfactory bulb
A
- not point to point
- quadrant to quadrant
- defined by boundaries of OR expression zones
- dorsolateral zone projects to dorsolateral on bulb
16
Q
distribution of specific or expressing neurons
A
- one neuron has one OR type
- within a zone, can be homogeneous or clustered
- within a quadrant, axonal projections bring together the axon terminals of like neurons
- all of the neurons expressing on OR converge onto the same set of glomeruli
- pattern from epithelium to bulb creates spatial code for stimuli across bulb
17
Q
organization summary
A
- one OR onto one glomerulus
- spatial patterns within and across zones
18
Q
step 1
A
- glomerulus is both anatomical and functional
- implied by connectivity
- unique pattern of responsiveness of individual ORs and pattern of activation of the bulb
- only maximally stimulate receptors send signals
- granule cells can block
- see picture
- D is stimulated by C8-comes through when compiled C8 from A,B,C
- glomeruli activated then mitral/tufted integrate
19
Q
step 2
A
-glomeruli are activated by odorants and different glomeruli by other odorants
20
Q
step 3
A
- like immune system
- each OR recognized odotope
- different ORs recognize different odotopes even if molecule is relatively the same-OH vs not
- one glomerulus is activated per odotope
- odors are identified and discriminated by the overall activation of glomeruli across the whole bulb
21
Q
cranial nerves and taste
A
- salt, sour, bitter, sweet, umami
- VII-chorda tympani, ant 2/3 tongue, greater superficial petrosal to palate
- IX-post 1/3
- X-epiglottis
- each axon innervates from 2-10 taste cells
- gustatory axons innervate the NTS
22
Q
central taste projections
A
- the NTS has projections to the ventral posterior medial nucleus of the thalamus (VPM), hypothalamus, amygdala
- VPM, hypothalamus and amygdala project to the insula and the frontal cortex
23
Q
basic taste pathways
A
- CN to NTS
- to VPM of thalamus
- NTS also to hypo and amygdala back and forht
- VPM to insula and frontal cortex
- connection to amygdala
24
Q
taste papillae
A
- 4 fields- circumvallate, foliate, fungiform papillae, taste buds on soft palate
- all taste fields respond to all tastants, but are more sensitive to some in certain areas
25
Q
trench and taste bud
A
- papillas have trench around them with taste buds in trench
- taste buds have many cell types
- taste buds are pear shaped collections of cells surrounded by BL that are embeded in stratified squamous epithelium
- each has 50-100 cells that include receptors and basal
- taste receptor cells make synapses in periphery
- microvilli of a taste cell extends through a taste pore
- gustatory afferent axons synapse with receptor cells
- stimuli cause depol with produce synaptic transmission across the receptor cell-axon synapse
26
Q
salt transduction
A
- ionic
- intracellular release in calcium and transmitter release
- amiloride sensitive
27
Q
acids
A
- hydrogen sensitive channels
- also ionic transduction mechanism which increases Ca and transmitter release
28
Q
sweet
A
- G coupled
- inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
- T1R2 and T1R3
29
Q
umami
A
- G coupled
- inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
- T1R1 and T1R3
30
Q
bitter
A
- G coupled
- inc cAMP, stimulates TRPM5 Ca channel (in membrane) via IP3
- T2R
31
Q
across neuron
A
- patterned reception
- single axons respond to many different primary stimulus quantities although they will have a preferential maximal response to one
- when recording from chorda tympani, differential firing pattern across pop-pattern
- same group of axons can differentially encode the stimulus quality
32
Q
labeled line
A
- banana receptor
- KO- lose all, but can restore singular functions
33
Q
Trigem
A
- oral irritation
- pungency
- don’t use alcohol to test smell- trigem
